Using normal euploid cells in culture, we propose to continue research pertinent to X inactivation and control of cell phenotype. We will determine if the entire X is subject to inactivation by analyzing clones from the heterozygotes for X-linked variants. We will attempt to isolate X specific DNA from human cells. In search of genetical heterogeneity, we will carry out complementation analysis in cell hybrids derived from phenotypically similar inborn errors of metabolism. We will look for segregants from human intraspecific hybrids carrying multiple genetic markers as a means to detect segregants and somatic recombination. We will continue to develop the D-valine selective system for epithelial cells which have D-amino acid oxidase, an enzyme present only in differentiated cells. We will continue studies of metabolic cooperation through intercellular communication.